ModelNotFoundException() : include called class name

There is no way to know which model is throwing `ModelNotFoundException()`.
With this simple cod change, the following is now possible:

```php
use Illuminate\Database\Eloquent\ModelNotFoundException;

App::error(function (ModelNotFoundException $e, $code)
{
	list($model, $tmp) = explode($e->getMessage(), ':', 2);

	switch ($model)
	{
		case 'User:':
			return Response::view('_errors.user_not_found', 404);

		case 'Project:':
			return Response::view('_errors.project_not_found', 404);

		default:
			return Response::view('_errors.404', 404);
	}
});
```